A. Field of the Invention
The present invention relates to a color image recording apparatus capable of forming a color image by repeating reciprocative transport of a recording medium with respect to a recording mechanism.
B. Description of the Prior Art
A known conventional color image recording apparatus is illustrated in FIGS. 28 through 39. Referring to FIG. 28, recording mechanism 101 comprises an electrostatic recording head 102, a driving circuit 114 connected thereto, and liquid developing devices 103a, 103b, 103c and 103d which are supplied black, cyan, magenta and yellow liquid developing agents, respectively. Each of the developing devices 103a, 103b, 103c, and 103d can be moved into and out of its respective developing position. Electrostatic recording paper 104 is provided with tracking lines 109a, 109b parallel to the edges of the recording paper 104, and registration marks 110a, 110b. Tracking lines 109a, 109b and registration marks 110a, 110b are shown in FIG. 28 on the upper surface of paper 104 for convenience, but would normally be provided on the lower surface of paper 104. Transport rollers 105, 106 serve to transport the electrostatic recording paper 104 in the either the forward or reverse direction, indicated by arrows D and E, respectively. A pinch roller 107 is provided above the recording head 102 for maintaining proper contact of the electrostatic recording paper 104 with the recording head 102. Between the first developing device 103a and the recording head 102, are line detectors 108a, 108b and mark detectors 111a, 111b which are disposed under the electrostatic recording paper 104 and fixed to the recording head 102 in such a manner to move together with the recording head 102. Line detectors 108a, 108b generate position signals of tracking lines 109a, 109b. Mark detectors 111a, 111b serve to detect passage of registration marks 110a, 110b. Recording-head positioning device 112 is equipped with pulse motors 113 and 117. Translation control circuit 116 controls pulse motor 113 to position the recording head 102 in the directions indicated by arrow F. Recording head control circuit 115 controls both the recording timing and the angle of the recording head 102.
Prior to recording an image using the first color, the electrostatic recording paper 104 is transported by the transport rollers 105, 106 in the direction of arrow D. Latent images corresponding to the tracking lines 109a, 109b and the registration marks 110a, 110b of a predetermined recording line pitch are recorded by the head 102 outside the effective area of the electrostatic recording paper 104. Thereafter such latent images are developed by the liquid developing device 103a supplied with a black liquid developing agent, so as to render visible the tracking lines 109a, 109b and the registration marks 110a, 110b. The electrostatic recording paper 104 with the tracking lines 109a, 109b and the registration marks 110a, 110b recorded completely thereon is then transported by the transport rollers 105, 106 in the direction of arrow E and is thereby returned to its former position.
The electrostatic recording paper 104 is then transported in the direction of an arrow D by the transport rollers 105, 106 again. At this time, the registration marks 110a, 110b are monitored by the mark detectors 111a, 111b respectively, constructed as shown in FIG. 29, such that light emitted from a light source 118 is converged by a lens 119 to illuminate the electrostatic recording paper 104. If the paper is positioned so that no registration mark 110a, 110b is currently under mark detector 111a, 111b, the light is reflected from the surface of the paper 104, and the reflected light is focused on the light sensitive surface of photosensor 121 through a lens 120. Alternatively, if one of the a registration marks 110a, 110b is under the mark detector 111a, 111b, the light emitted form light source 118 and reflected off the face of the paper 104 is reduced and photosensor 121 does not detect the reflection of light from the surface of paper 104.
As shown in FIG. 30, the photosensor 121 of mark detectors 111a, 111b comprises a light-receiving photo transistor 122, an operational amplifier 123 and a comparator 124. The output of the photo transistor 122 is amplified by the operational amplifier 123 to form a waveform as shown in FIG. 31. The output voltage of the operational amplifier 123 is converted by the comparator 124 into a binary signal shown in FIG. 32. As a result, the output signals of mark detectors 111a, 111b are high upon the detection of registration marks 110a, 110b and low when no registration marks are present.
When the mark detectors 111a, 111b first detect registration marks 110a, 110b along the longitudinal edges of the electrostatic recording paper 104, the recording head 102 begins to form a latent image corresponding to the black image. Alternatively, instead of starting the formation of the black latent image at the initial detection of the registration marks 110a, 110b, the latent image may be started after a predetermined time from the initial detection of the registration marks 110a, 111b. The outputs of the mark detectors 111a, 111b are fed to flip flops 125a, 125b respectively of a recording-head control circuit shown in FIG. 33. The outputs Q, of each of the flip-flops 125a, 125b alternately represent a mark interval (high level duration). The outputs Q, of the flip-flops 125a, 125b are connected to count enable inputs of counter circuits 126a, 126b, 126c, 126d to which output pulses from a pulse generator circuit 127 proportional to the length of motion of the electrostatic recording paper 104 are supplied as clock pulses. Accordingly the counter circuits 126a and 126b alternately measure the interval of the registration marks 110a, while the counter circuits 126c and 126d alternately measure the interval of the registration marks 110b. The results of such measurements are then fed to a divider circuit 128, and the counted values are compared with reference values (determined initially at the time of recording the registration marks 110a, 110b), whereby data for setting the next trigger generator circuit 129 is produced in such a manner that the distances between the registration marks 110a, 110b are always recorded with an equal number of lines (N lines in this example). On the basis of the data thus obtained, the trigger generator circuit 129 controls a driving circuit 114 in accordance with reference clock pulses 130, thereby generating a period during which an image is formed by the recording head 102.
Referring to FIG. 34, the operation described above will be described with reference to a timing chart with respect to registration marks 110a and mark detector 111a. The output of mark detector 111a is shown in FIG. 34(a). As in FIG. 32, a high signal indicates the presence of a registration mark 110a; a low signal indicates the absence of a registration mark. The outputs Q, of the flip flop 125a are shown in FIGS. 34(c) and 34(d) respectively. The counter circuits 126a and 126b function during the high level of the outputs Q, and count the reference pulses obtained from the pulse generator circuit 127. That is, the counter circuit 126a counts the reference pulses during the periods t.sub.1, t.sub.3, t.sub.5, . . . between the odd numbered registration marks 110b, while the counter circuit 126b counts the reference pulses in the periods t.sub.2, t.sub.4, t.sub.6, . . . between the even numbered registration marks 110b. The divider circuit 128 divides the periods t.sub.1, t.sub.2, t.sub.3, . . . by the number of lines N to determine the distance between the registration marks 110b. The resultant values, t.sub.1 /N, t.sub.2 /N, t.sub.3 /N, . . . , are output from the divider circuit 128 to the trigger generator circuit 129 after measuring the distance between each successive pair of registration marks 110b.
The trigger generator circuit 129 outputs trigger signals of period t.sub.n /N during the period of t.sub.n+1. These signals of t.sub.1 /N, t.sub.2 /N, t.sub.3 /N, . . . t.sub.n-1 /N, t.sub.n /N corresponding to the values obtained from the divider circuit 128, are shown in FIG. 34(b). The driving circuit 114 energizes the recording head 102 synchronously with such trigger signals, thereby forming a latent image on the electrostatic recording paper 104 every t.sub.n /N period.
Furthermore, when the registration marks 110a, 110b are detected by the mark detectors 111a, 111b, the positional difference between the corresponding registration marks 110a, 110b on opposite edges of paper 104 is detected by a difference detector circuit 131. In accordance with the difference thus detected, a motor control circuit 132 feeds a signal to pulse motor circuit 133 to operate pulse motor 117. Pulse motor 117 adjusts the rotational position of recording head 102 such that the mark detectors 111a, 111b, which are fixed to recording head 102, are positioned to detect registration marks 110a, 110b simultaneously.
Simultaneously with the detection of the registration marks 110a, 110b by the mark detectors 111a, 111b, the deviation of the tracking lines 109a, 109b from their reference positions are detected by the line detectors 108a, 108b, respectively, which are constructed as illustrated in FIG. 35. Each line detector 108a, 108b is comprised of two photosensors 134a, 134b and positioned so that the tracking lines 109a, 109b pass between the photosensors 134a, 134b. Light emitted from a light source 131 is converged on the electrostatic recording paper 104 by a lens 132. The light reflected from the face of paper 104 is focused onto the light sensitive surface of two photosensors 134a, 134b by a condenser lens 133. Each photosensor 134a, 134b comprises a photo transistor 135 and an operational amplifier 136 as shown in FIG. 36. The amount of light received by the photosensors 134a, 134b is converted into a voltage output. The output of each operational amplifier 136 changes in accordance with the amount of light reflected from the face of paper 104 as graphically shown in FIG. 37.
The translational positioning of the recording head 102 is accomplished as follows. FIG. 38(a) illustrates a state where the tracking line 109a or 109b is properly positioned with respect to the line detector 108a or 108b. In this state, the tracking line 109a is uniformly detected by the two photosensors 134a and 134b, so that the output voltages of both photosensors 134a, 134b are equal to each other as graphically shown in FIG. 38(d). If the tracking line 109a is deviated to the left as illustrated in FIG. 38(b), the amount of light received by the photosensor 134a is reduced while the amount of light received by photosensor 134b is increased; the output voltage of the photosensors 134a, 134b are correspondingly affected as shown graphically in FIG. 38(e). If the tracking line 109a is deviated to the right as illustrated in FIG. 38(c), the amount of light received by the photosensor 134a while the amount of light received by photosensor 134b is reduced; the output voltages of photosensors 134a, 134b are correspondingly affected as shown graphically in FIG. 38(f).
The output signals of the line detectors 108a, 108b are fed to comparator circuits 135a and 135b, respectively, of the translation controller 116 as shown in FIG. 39. The output voltages of the two photosensors 134a, 134b of each of the line detectors 108a, 108b are compared. In accordance with the result of such comparison, correction signal generator circuit 136 determines the correction to be made to the position of the recording head 102 and line detectors 108a, 108b fixed to the recording head 102, with respect to the electrostatic recording paper 104. A control signal is fed to a pulse motor driving circuit 137 to control pulse motor 113 for causing translational motion of the recording head 102 in such a manner as to maintain a balanced state in the output voltages of the photosensors 134a, 134b of the line detectors 108a, 108b as graphically shown in FIG. 38(d). As a result, the output voltages of the photosensors 134a, 134b in each of the line detectors 108a, 108b are placed in a balanced state, and the pulse motor 113 is brought to a halt upon detection of such state by the correction signal generator circuit 136 of the translational controller 116.
This operation is performed until the first color image, usually black, has been completed. The paper 104 is then moved by the transport rollers 105, 106 back again in the direction of arrow E (FIG. 28) until it reaches its initial position. On subsequent passes of the paper 104 through the apparatus, the registration marks 110a, 110b and the tracking lines 109a, 109b are detected in the same manner to superimpose the latent images of the other colors on the previously formed image. The operation is repeated for cyan, magenta, and yellow until the complete color image has been formed.
One disadvantage of the known apparatus just described is that the tracking lines 109a, 109b and registration marks 110a, 110b require a substantial portion of the paper 104. The edges of the paper 104 which are used by the tracking lines 109a, 109b and registration marks 110a, 110b are not available for image recording. Another disadvantage of the apparatus described is that the positioning of the paper 104 in the transport direction is controlled by first measuring the distance between the registration marks and then determining the recording timing on the basis of such measured information. Any error induced during the transport of the paper 104, such as slippage of the transport roller or the like, is corrected on the basis of the deviation in the recorded image formed thereafter, hence causing a positional color discrepancy when many colors are superimposed upon one another. In addition, the process of positioning the recording head perpendicular to the transport direction of the paper 104 by monitoring the tracking lines 109a, 109b is subject to inaccuracies due to non-uniformity of the tracking lines. The mechanism may attempt to correct the position of the recording head 102 in response to a non-uniformity sensed by the photosensors 134a, 134b even thought the position of paper 104 is unchanged. Finally, the mechanism required for effecting translational and rotational motion of the recording head 102 is complex leading to a likelihood of failure.